1. Field of the Invention
This invention relates to a process for the polymerization of 1-alkynes. More specifically, this invention relates to a process employing a two component catalyst system for the polymerization of acetylene. The first component is a transition metal complex and the second component or co-catalyst is an organometallic compound containing an element from Group 1a, 2a or 3a.
2. Description of the Prior Art
Polyacetylene is a linear polymer of acetylene having alternative single and double bonds. It is electrically conductive and this property can be enhanced or inhibited by appropriate doping with electron acceptors (such as arsenic pentafluoride or a halogen) or with electron donors (such as lithium or sodium). Thus polyacetylene can be made to have a wide range of electrical conductivity. Uses for polyacetylene range from insulators to n- or p-type semiconductors, to strongly conductive forms. Polyacetylene can be made in the form of fibers and thin films. Though still in the experimental stage, these polymers have significant possibilities for industrial applications. Structurally, polyacetylene exists in two isomeric forms: ##STR1## The polymerization of acetylene typically provides a mixture of both structures in the polymer backbone.
The conductivity of polyacetylene fibers increase with the degree of orientation. Increased orientation is therefore preferable. Since acetylene polymerizations yield a mixture of cis- and trans- structure in the polyacetylene backbone, there has been considerable experimentation in recent years in processes and catalysts, which will provide highly stereo specific polyacetylene.
In part the instant invention relates to a novel transition metal catalyst useful for the polymerization of acetylene. The use of transition metal catalysts for the polymerization of acetylene and 1-alkynes has long been known. Catalysts suitable for this type of polymerization were first described by G. Natta et al. in Italian Pat. No. 530,753 of July 15, 1955. Watson, McMordie and Lands, Journal of Polymer Science, Vol. 55, page 137, John Wiley and Sons, 1961, later described several catalysts useful for the polymerization of acetylene.
It is characteristic of these prior art catalysts that the structure of the resulting polyacetylenes varies with the reaction temperature and the co-catalyst to catalyst ratio, as well as with the particular transition metal catalyst selected. For example, it has been reported that a Ziegler-Natta catalyst of the formula Ti/Al(C.sub.2 H.sub.5).sub.3, produces high cis-polyacetylene only at temperatures of 0.degree. C. and below, while high trans-polyacetylene is produced at 100.degree. C. and above, at an Al:Ti ratio of 4:1, Ita, Shirakawa and Ikeda, Journal of Polymer Science - Polymer Chemistry Edition, Volume 12, page 11, 1974.
It is an object of the instant invention to develop a novel catalyst and catalytic process for the polymerization of acetylene.
It is an object of the instant invention to develop a catalytic process which produces highly stereospecific at modest temperatures.
It is also an object of the instant invention to develop a catalytic process which will permit the control of the polymer microstructure so that high-cis or high-trans or intermediate structures of polyacetylene may be produced.